In recent years, many efforts have been made widely for suppressing a peak of a power load for power load leveling.
Leveling a power load allows stable power supply from a power supplier (such as electric power company) and can eliminate the necessity for preparation of excessive electric power generation equipment costs for a power load peak. Shifting daytime power loads to the nighttime in which a lower proportion of power is generated by thermal power generation can reduce the amount of carbon dioxide exhausted when a unit amount of electricity is generated. On the other hand, a power consumer (such as an office and a factory) can advantageously reduce the power receiving equipment costs and/or electricity charge.
By the way, in order to level power loads, a power consumer may prepare a battery, and the battery is discharged in a time zone with a large power load so that the peak value of power to be supplied from a commercial power supply can be suppressed.
For example, when power supplied from a commercial system exceeds a predetermined value, the excess amount of power may be discharged from a power storage device so as to control the power to be supplied from a commercial system so as not to be higher than a desirable value (target demand value). However, according to this technology, the discharging from a power storage device may not address a power demand increase which is much higher than expected. For that, power which is greatly higher than the desirable value is supplied from the commercial system.
Reference may be made to Japanese Laid-open Patent Publication No. 2003-244840.